Butadiene polymers as elastomer additives



Patented May 12, 1953 BUTADIENE POLYMERS AS I ELASTOMER ADDITIVES Willie W. Crouch, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application January 2, 1951,

' Serial No. 204,069

11 Claims.

This invention relates to elastomer compounding. In a more specific aspect this invention relates to new plasticizers and/or tackifiers for elastomers, synthetic and/or natural. In a still more specific aspect this invention relates to polybutadienes as softeners, plasticizers and/or tackifiers for synthetic and/ or natural rubber.

Various types of materials have been employed as softeners, tackifiers and/or plasticizers for both natural and synthetic rubbers and it is known that variations in properties of rubber products can be produced through the use of different plasticizing agents. A good plasticizer, in addition to softening a rubber stock, must give a finished product with other desirable properties. Some materials which exert the desired plasticizing action often have deleterious effects on other properties to the extent that the finished products are of little value for many purposes. It has generally been recognized that high Mooney value elastomers are diflicult to process and large amounts of softeners are usually required. The presence of sufficient plasticizing agent to provide desirable processing characteristics frequently results in detrimental effects on physical properties. Also, many synthetic elastomers do not possess suflicient tack to be used in carcass stocks.

I have now discovered that liquid butadiene polym ars, prepared under carefully controlled mass polymerization conditions in the presence of an alkali metal and /or alkali metal hydride catalyst, serve as excellent rubber plasticizers. These plasticizers comprise liquid polymers prepared from conjugated diolefin hydrocarbons selected from the group consisting of 1,3-butadiene and 2methyl-1,3-butadiene, or isoprene. The method for the preparation of these polymers is described in my copending application filed December 23, 1948, Serial No. 67,098, of which this case is a continuation-in-part. The new plasticizers, tackifiers or softeners used in the practice of my invention can very advantageously be used in carcasses wherein synthetic elastomers are used.

It is an object of this invention to provide new elastomer compounding methods and additives and elastomer mixes.

Another object of this invention is to provide bonds.

new elastomer compounding additives and new elastomer products resulting from their use.

It isanother object of this invention to provide new softeners, plasticizers and/or tackifiers for elastomers, synthetic and/or natural, and new elastomer products with improved properties resulting from the use of such softeners, plasticizers and/or tackifiers.

Other objects and advantages of this invention will become apparent, to one skilled in the art, upon reading this disclosure.

The term rubber, as used in this disclosure, is intended to cover both natural and synthetic rubber. In its broadest aspect, my invention applies to providing softeners, plasticizers or tackifiers for vulcanizable organic elastomers containing unsaturated carbon to carbon My invention applies to softening, plasticizing or tackifying natural rubber or rubber-like polymers produced by the polymerization of aliphatic conjugated diolefins, particularly those having from 4 to 6 carbon atoms per molecule, such as butadiene, isoprene, pentadienes, etc., or the co-polymerization of such diolefins with a compound containing a CH2=C group copolymerizable therewith, such as styrene, acrylonitrile, etc. The vulcanizable plasticizers used in the practice of my invention are very advantageously applied to the compounding of the relatively new low-temperature synthetic rubbers which are prepared by copolymerizing butadiene and styrene monomers in an emulsion system at a temperature of from 20 to 15 C., the butadiene monomer being present in an amount of from to weight per cent of the total weight of monomers charged. The softeners, plasticizers, or tackifiers of my invention can be used with butyl rubber stocks which are produced by co-polymerizing a major quantity of isobutylene, with a minor quantity of a conjugated diolefin, such as those mentioned hereinbefore. The softeners, plasticizers, or tackifiers of my invention can be used with reclaimed natural or synthetic rubbers and to various mixtures of natural, synthetic, reclaimed natural and reclaimed synthetic rubber.

, The plasticizing or softening agents of this invention are applicable in compounding both natural and synthetic rubbers. Their powerful plasticizing action makes them particularly 3 valuable for use in high Mooney value butadienestyrene elastomers which are generally regarded as being difrlcult to process. When so used they produce rubbers which are not only readily processable, but which have good physical properties and are generally superior in aged flex life, abrasion resistance, and extrusion characteristics.

Similar effects are also produced in the properties of lower Mooney butadiene-styrene elastomers. These plasticizing agents are also valuable for use in rubbers of the Perbunan type, i. e., butadiene-acrylonitrile copolymers, since they give products which show high swelling and low extractability characteristics. One of the chief advantages of these plasticizers is that they are vulcanizable, i. e., they undergo vulcanization along with the rubber and become thoroughly incorporated in the vulcanizate. In this respect they differ from many of the commercial plas ticizers which are not vulcanizable and therefore remain as unconverted materials in the finished product. They have been found to be more effective in their plasticim'ng action than many of the commercial softeners, a smaller quantity being required to give a product with the same compounded Mooney value as is obtained with a much larger quantity of a commercial softener. These softeners can be incorporated into the rubber on a mill, in a Banbury mixer, etc, or if preferred, they can be added to the latex. Ihey can be added to the rubber before, during or after addition of other compounding ingredients. The liquid polybutadiene and liquid polyisoprene which are employed as vulcanizable plasticizers in the practice of my invention are not rubber-like synthetic polymers, but are non-rubber-like liquid polymers free from solid polymers. The molecular Weight of these compounds is usually within the limits of 800 to 3000 when determined in a solvent, and they usually have a viscosity of 100 to 5000 Saybolt Furol seconds at 100 F. Unsaturation can be determined by the iodine monochloride method of Kolthofi (Lee, Kolthoif, and Mairs,

J. Polymer Science 3, No. 1, 66 (1948) if desired.

with or without an inert reaction medium and I catalyzed by a finely divided alkali metal and/or alkali metal hydride, such as sodium, potassium, lithium, sodium hydride, potassium hydride, lithium hydride, and the like. Polymers thus prepared contain no modifier or viscosity controlling agent and they are also free from materials which would act as inhibitors such as antioxidants and shortstops. Finely divided catalyst is used, preferably with a particle size below 200 microns, more preferably below 100 microns in the range of 40 to 80 microns. The amount of catalyst employed usually does not exceed 2 parts by weight of the total monomer charged, preferably in the range 0.5 to 1.5 parts by weight per 100 parts monomer. When mass polymerization methods are employed, liquid products are readily obtained by controlling th temperature, pressure, amount of catalyst, kind and amount of solvent, and the like, with no additional materials being necessary to control the viscosity.

The polymerization is usually carried out in the presence of a solvent, such as parafiinic hydrocarbons, especially the light normally liquid paraffins such as pentanes, hexanes, heptanes; certain naphtha fractions, preferably having not over 10 carbon atoms per molecule; cycloparaffins such as cyclohexane; aromatic hydrocarbons such as benzene, toluene, other lower allrylbenzenes; and the like. The preferred temperature for carrying out the polymerization lies in the range from 60 to 110 C. However, a narrower temperature range of from to C. is most frequently chosen. A more complete description of the process of making these vulcanizable plasticizers which are used in practicing my invention can be found in my copending application, Serial No. 67,098, filed December 23, 1948, of which this application is a continuation-in-part.

The amount of liquid vulcanizable plasticizer employed will vary depending upon the type of polymer being processed and the properties desired in the finished product. It will usually be in the range from 3 to 25 parts by weight per 100 parts by weight elastomer, th larger amounts being used for high Mooney viscosity materials.

Vulcanizable organic elastomer compositions usually contain fillers; modifiers; softeners, tackifiers, and plasticizing substances; vulcanizing agents; age resistors or antioxidants; and accelerators of vulcanization. The exact composition of the vulcanizable organic elastomer composition depends upon the use to which the vulcanizable composition is to be put. The new softeners, plasticizers or tackifiers of my invention can be used in all of the commonly used compounding recipes.

Carbon black is added to many vulcanizable organic elastomer mixes during compounding as a filler. There are many types of carbon blacks used today in compounding, among which are: recently developed high pH furnace carbon blacks havin a pH of from 8.0 to 10.5, usually 8.6 to 10.1, such as high abrasion furnace carbon blacks (HAP blacks), super abrasion furnace blacks (SAF blacks) and high modulus furnace carbon blacks (HMF blacks) reinforcing furnace blacks (RF blacks) and very fine furnace blacks (VF? blacks) easy, medium, or hard processing channel. blacks; lamp blacks; fine and medium thermal carbon blacks; acetylene carbon blacks; semireinforcing furnace carbon blacks; conductive furnace and conductive channel carbon blacks; and high elongation furnace carbon blacks. Other pigments or additives, such as ferric oxide, magnesium carbonate, titanium dioxide, zinc oxide, hydrated alumina, kieselguhr, slate dust, zinc peroxide, zinc chloride, lead peroxide, lead oxide, chlorinated parafiins, glue, barytes, fossil flour, lithopone, various clays, finely divided silica, Whiting, etc., can be added as fillers or to modify the properties of the vulcanizable composition or vulcanized composition, such properties as the rate of cure, resistance to scorching during processing, activation of acceleration, etc.

Other softeners, tackifiers and plasticizing substances can be used in conjunction with the softeners, tackifiers and plasticizing materials of this invention, if desired. There are many such substances, among which are vegetable oils, such as palm oil, rape oil, olive oil, linseed oil, castor bean oil, soya bean oil, tung oil; bitumens including so-called mineral rubbers, which comprise natural products, such as gilsonite, rafaelite, and also high-boiling petroleum residues, asphalts, etc; pine tar; paramn wax; mineral oils; may acids, such as" 'oleic acid', stearic acid,

palmitic "acid; lauricacid'; etc; c'eresin; I naphthalenes; rosin; wool grease; carnauba wax; the many organic chemical compounds, such as glycerol, glyceryl monostearate, glyceryl monooleate, glyceryl. monoricinoleate, trioctyl. phosphate, triglycol dioctoate, ethylene glycol monostearate and the monooleate, phenol-formaldehyde thermosetting resins, poly-alpha-methyl Styrene aI-id other polymers of styrene and "substituted; sebacate, polybutenes, zinc resinate, cpumarone resins, dihydroabietic acid, etc. Most of these compounds'aid'tackiness as well as soften or plasticize the vulcanizable organic elastomers. Also, some of them teristics. Z

styrene, dioc tylphthalate, dioctyl exhibit. modifying charac- 1 Vulcanizing agents'are added to vulcanize the organicielastomers during the vulcanization step of processing. .There are a Wide variety of vulcanizing agents, such as: sulfur, including powdered sulfur, or in one or more other forms, and Y mixtures thereof; so-called plastic sulfurs; sulfur-containing compounds, such as sulfur chloride, hydrogen sulfide, sulfur thiocyanate, tetraalkylthiuram disulfides, etc.; selenium; tellurium;

benzoyl peroxide; trinitrobe'nzene; dinitr'obenzene; nitrobenzene; quinones'; certain inorganicdiazoaminobenzene and its oxidizing agents; derivatives; other nitrogen-containing compounds, etc. I V

Y Accelerators ofvulcanization are added to ac-, celerate vulcanization-during the vulcanization step of processing. There are many well known accelerators of vulcanization, such as: thioureas; thiophenols; mercaptans; dithiocarbamates; xanthates; trithiocarbamates; dithio acids, mercaptothiazoles; mercaptobenzothiazoles; thiuram sulfides; organic-cobalt chelates; etc., and vari ous mixtures thereof. Some widely used and particularly good accelerators are, for instance, mercaptobenzothiazole, benzothiazyl disulfide, di-

phenylguanidine, zinc salt of mercaptobenzothia'' zole, zinc benzothiazyl sulfide, tetramethylthiuram disulfide. Necyclohexyl-2-benzothiazole sulfenamide, aldehyde ammonias, triphenylguanidine, zinc dibutyl and zinc dimethyl dithiocarbamate, many others,'and mixtures thereof.

In most casesit is ,the usual practice to add-age resistors or antioxidants to vulcanizable organic elastomer mixes during themixing stepof processing in order. to slow down org'prevent the deterioration off the vulcanized product. Antioxidants or age resistors have thepropertyof main-- taining tensileistrength, .resi-stance to abrasion;

elasticity, prefve'ntin'g' flex' cra,.cl ring:,fetc.- One or more antioxidants are usually employed, such as phenyl-beta-naphthylamine, p-ami'nophenol,fhydroquinone, p-hydroxydiphenyl, diphenylamine, 2,4-toluene 'diamine; p-ditdlylamine, 'o-ditolyamine, beta-naphthyl-nitrosoamine, N,N-diphenyl diamine ethane, phenyl-alpha-naphthyl-- amine, p,pf-diamino-diphenylmethane, etc.

The vulcanizable organic elastomer compositions resulting from admixing the various ingredients with the new softeners, plasticizers and tackifiers of myinvention .by the methods known in the prior artiare vulcanized in the usual manner after. they/are moldd or 'shapedinto' the' desired shape; by the. numerous shaping opera-' printers blankets, engraving plates,

6 example, they can -be,used.for tire tubes, tire treads, tire casings, shoe soles and heels, raincoats, table covers, hose for the transmission of fluids, belts, balloon coverings, printers rolls, aprons, gloves, masks, tanks, battery cases, friction tape mats, wire insulation, etc. Fabrics can be coated or impregnated b-y calendering or impregnation with a suitable emulsion.

The following are set forth as examples of my invention. It is to be understood that the quantities, materials, etc., set forth in the following examples, are not to unduly limit the scope of my invention.

1 Dresinate 214-. 2 Triton R-100.

Polymerization was continued to 60 percent co'n-' version and the resulting polymer had a raw Mooney value of to 55.

Samples of the polymer prepared as described,

above were employed in a compounding study using variable quantities of liquid polybutadiene softener (viscosity 377 Saybolt Furol seconds at 100 F.) at different black loadings. Black quantities of 25, 50, 60, and 75 parts by weight. per 100 parts rubber were used and the softener quantities were 5, 10, and 15 parts by weight per 100 parts rubber at the low loading of black and .10, 25, and 50 parts by weight per 100 parts rubber at the three higher concentrations of black. 5 F-or purposes of comparison an asphalt type softener (Asphalt #6) was evaluated at the same levels to serve as a control for the stocks con- .taining the vulcanizable liquid polybutadiene Part Elastomer fi 3 Carbon black 25, 50 60 '75 Zinc oxid e Q i 30 Stearic acid 1'0 Sulfur 17 5 'i-Flexamine 1.0

"softener. Stocks were compounded according to the followingbasic recipe and were roll mill mixed:

= 2 Liquid polybutadiene or asphalt tions of the prior art, such as calendering, casting from solution, continuous of-discontinuous" extrusion, molding in open or closed molds, etc., and they can be used for the many purposes for which other similar compositions are used. For

softener .5, 10, 15, 25, 50 Santocure 3 variable A Philblacl 0, a abrasion furnace ca qis t Angnrglfi toxgilc powtli r sp. gr. 1.10, M. P. 75 55 5 561- 1 a iysica mix ure contain complex diary lamme-ketone reaction mg per cent of a cergt of N.N-d1phenyl-pphenylene-diamine. N-cyclohexyl-2-benz0thiazole-sulfenamide.

product and '35 per the compounded Mooney values.

WITH {TULOANIZED SOFTENER ..,Wett Hours Power 1 1 Tack Sample No.

Mill Re nill It isnote'd that the liquid polybutadiene softener exerted. a much more. powerful plasticizing action than the asphalt softener as evidenced by On the basis of compounded Mooney values, 10 and 25 parts (per 100 parts elastomer) of vulcanizable plasticizer was found to be approximately equal to 25 and.50.parts (per 100partselastomer) of asphalt softener in .plasticizing action. The vulcanizable softener also exerted a much more pronounced effect on the Shore hardness values. Both unaged and aged samples containing polybutadiene showed superior. abrasion resistance to the samples containing the asphalt softener; also the aged flex life values for samples containing polybutadiene were-superior: to those. containing. equal quantities of asphalt softener at black loadings of 60 parts per 100 parts elastomer and below. If the properties of compounds of equal processability (equal compounded Mooney) atthe same black loadings, are compared, it can be seen that the stocks softened with vulcanizable plasticizer exhibited higher modulus and better resilience (e. g., compare the followin 'samples: 1 and 4 and 17; '7 and 20; 11 and 24).

7 Example H j Liquid polybutadiene (as in Example I) was employed as a softenr'for' af135 Mooney butadiene/styrene elastomer prepared by emulsion polymerization at 5 C. in an ironpyrophosphate activated recipe catalyzed by cumene hydroper- Philblack 0, a high abrasion furnace car llon black.

.at 307 F. and the physical properties determined. The following results were obtamed:

Liquid Paraflux- Polybiita- Circo Oil dieiie Blend Unaged Samples: I

Compounded Mooney, MS 1%.. 35. 3 43. 1 Stress-strau1 properties at F.--

300 percent Mpdulus,p s i 410 520 Tensile, p. s. i 2, 3, 120 Elongation, ercen 680 760 Hysteresis, AT, F 1 88. 3 88.3 Resilience, percent '63. 9 65. 4 Flex life at 210 F., M- 36. 2 1 45. 7 Shore hardness. 50. 5 52. 5 Abrasion loss, cc 2. 76 3. 40 Compression set, perce 20. 7 20. 4 Extrus on at 250. F., inches/minute. 61. 5 42 Extrusion at 250 F., ccJminute 97. 8 77-. 6 1 Tack rating 7 5 Stress-strain properties at 80 F.-- i

300 percent modulus, p. s. i l, 300 1, 660 Tensile, p. s. i l, 630 3, 600 Elongation, percent; 350 510 Hysteresis, AT, F 1 66. 5 l 55. 0 Resilience, percent 67. 9 Flex life at 210 F., M 11. 4 5. 73 Shore hardness 56 61 Abrasion loss 3. 49 .3. 57

1 45 minute cure. I 2 Percent broken at 50,000 fle iures.

The above data show that the liquid' polybuta diene was a much more powerful plastici'zer than'the commercial softener blend and there'- sulting compounded stock was markedly superior .in agedflexlife and also more resistant to abrasion than the sample containing. the commercial soitener. .blend,.and .extrudedat amore rapid ra e. i 1

" V v Erdmple III I Parts by weight Elastomer; *ML-4 -100 Liquid polybutadiene 9.9 Carbon black 50 Zinc oxide 3 Sulfur 1.75 N cyclohexyl 2 benzothiazolesulfenamide 0.95 Stearic acid 1.0

v 1 Philblack 0, as described hereinbefore.

For comparative purposes a control was run usmg 10 parts of a commercial asphalt, softener (asphalt #6).

The mixes were milled and cured at 307 F. to

.equal states ofcure ('17 per cent compression set) and the physical properties determined. The following results were obtained.

Liquid Polybuts Asphalt-#6 diene Unsed Samples: 6

oinpounded Mooney, MS 1 52.5 64. 5 Minutes cure to 17% Compression set 31 29 Stress-strain properties at 80 F.-

300% modulus, p. s. i 1, 270 1,360 Tensile, p. s. i.- 3, 960 4,000 Elongation, percent 575 610 Hysteresis, AT, F.- 76.4 82.0 Resilience, percent 66. 1 62. 0

Flex life at 210 F., M 11. 2 19. 2

Shore hardness 57. 5 62. -5

Abrasion loss, cc. 2. 78 2. 20

Extrusion at 250 F., inches/minute. 40. 0 35. 0

Extrusion at 250 F., cc./minute 76.4 67. 4 Oven Aged 24 Hours at 212 F.:

Stress-strain properties at 80 F.-

300% modulus, p. s. i 2, 4.00 2, 210 Tensile, p. s. i 3, 500 3, 840 Elongation, percent. 420 425 Hysteresis, AT, "F 58 62. 6 Resilience, percent 71.3 66.6 Flex life at 210 F., M as 3.0 Shore hardness 65 67 Abrasion loss, cc. 2. 62 2.82

35 minute cure.

These data show that the aged samples containing liquid polybutadiene are superior to stocks 25 containing asphalt softener in modulus, heat build-up, resilience, flex life, and abrasion. loss. The liquid polybutadiene is also shown to be a much more powerful plasticizer than the asphalt softener.

Example IV A 55 Mooney, ML-e, butadiene/styrene copolymer was prepared by emulsion polymerization at 5 C. in an iron pyrophosphate activated recipe 0 using cumene hydroperoxide as the catalyst. Liquid polybutadiene (as in Example I) was employed as. the softener and was added to the latex, 5 and 10 parts, respectively, being used per 1.00 parts. rubber. The compounding recipe was as. follows:

Parts by weight .Bntadiene/styrene elastomer 100 Pelybutadiene 5.10 Carbon black 50 Zinc oxide 3 Stearic acid 1 Sulfur 1.75 N cyclohexyl 2 benzothiazolesulfenamide--- 0.95

1 Philblack O, as described hereinbefore.

For comparative purposes a control was run usins 6 Parts of. a. commercial asphalt softener (asphalt #6) instead of the liquid polybutadiene. The rubber stock was similar to that used above except that the raw Mooney was 54.

The mixes were milled and cured 30: minutes at 307 F. Physical properties were determined and the following results obtained;

, .Liquidlfolybuta: dime Asphalt.

' fiParts 10Perts Unaged Samples:

compounded Mooney, MS 1%" 48 41 55 Stress-strain properties at 80 'aoo%.Mo m1us,. .s. 1 ,900 i 1 2,080 Tensile, p. s. 3,680- 3,540 a, 650 Elongation, percent 480 540 480 sti ess-strain properties at 200 Tensile, p. s: i 2, 280 1, 730 2, 230 Elongation, percent, 300. 305 265 Hysteresis, AT, F., 70 71. 6 71. 6 Resilience, percent 6214 60.5' 59.7 Flex life at 210 M. 7.1 4-9.. 8.4 Shore hardness; 62.5 59 65 '76 Liquid lolybuta- Asphalt 5 Parts 10 Parts Unaged Samples-Continued.

Stress-strain properties at 200 F.Oontin Abrasion loss, grams 1 .1 2. 38 2. 79 2.86 Compression set, percent. 13. 1 14. 6 16.1 Extrusionat'250 F inches] i minute 40.5 41 35. 5 Extrusionat250 F'.,-gramsl minu 99.5 100. 5 89:5 Oven Aged 24 Hours at 212' 1.:

Stress-strain properties at 300% modulus, p, s. i .3, 2,630 3.230 Tensile, p. s. i.. 800 3,460 600 Elongation, percent 350 370 330 Hysteresis, AT, F... 60. .8 62. 5 64.8 Resilience, percenin 68.8 67.6 66. 8 Flex life at 210 F 6. 4 6. 2 6. 0 Shore hardness- 6T '64 69. 5 Abrasion loss, grams 2. 53 1 2.82 3. 31

1 45'minute euro. 1 35 minute cure.

Butadiene/styrene elastomer 100.

Carbon black '50 Zinc oxide 3.0 Polyisoprene 6.0 Stearic acid- 1.0 Flexamine 1 1.0 Sulfur 1,75

N-cyclohexyl-2-benzothiazolesulfenamide.

-Asdescribed in- Example I.

A control run was made using 6 parts ofa commercial asphalt softener (asphalt #6)" instead of liquid polyisoprene.

Physical properties were determined after ourmg the samples at 307 F. for 30 minutes. The results were as follows:

: Bolyisd pram, Asphalt.

Unaged Samples:

Oompounded Mooney, MS 1% 38. 5 44 Stress-strain roperties at 80 300% Mo ulus, p s 1, 380 1, 520 Tensile, p. s. 3,360 J20 Elongatromgerceniu.-- 570- 5 585 Hysteresis, AT, '85. 6 78. 0 Resilience, percent 57. 4 58; 3 Flex life-at 210* E.,,M 13. 2: J 16. 8 Shore.hardness...-.- 68. 60 Abrasion loss, grams. 1.73 Compression set, percent 20. 7 1D. 6 Extrusion at 25.0? F., inches/minute. 36. 5 34. 8 Extrusi'onat250 F., grams/minute.-- 98. 5 94. 5 Oven Aged 24rH'qurs1'at 212 Y Stress-strain properties at 80 F.

300%;modulus, p. s i. 2,875 Z860 Tensile, p. s. 1 3, 480. 3,380 Elongation, percent. 370 375 Hysteresis, AT, F... 61.2 641 9 Resilience, percent 65.2 6d. 8 Flex LiIe at 210?F'., M.. 8; 5' j 516 ,Shorehardness 65 I 65 Abr ion loss, grams 1 2. 35 2. 74

Example VI Liquid polybutadiene (as in Example I) was compared with th commercial softener, Dutrex 6 (aromatic nucleus with attached unsaturated olefins: odorless, non-toxic, dark, heavy, viscous liquid, sp. gr., 1.03; M. P., 60 F.; B. P. 610 F.) and with a blend containing equal parts of Circosol 2XH (a petroleum hydrocarbon softener, containing hydrocarbons of high molecular weight, in the form of a heavy, viscous, transparent, pale green, odorless liquid of low volatility; sp. gr., 0.940; Saybolt viscosity at 100 F., about 2,000 seconds) and Parafiux (an asphaltic flux). These softeners were employed in a 50- 55 ML-4 rubber stock prepared as described in Example I and compounded according to the recipe given in Example V except that in each case 10 parts softener was used. The samples were cured at 307 F. for 45 minutes and the physical properties determined. The results are shown below.

i Circosol Liquid Polybuta- Dutrex i g diene Blend Un ed Samples:

ompounded Mooney, MS 1% 42. 5 44 47 Stessi strain properties at 300% modulus, p s 1-- 1,250 1, 410 1,380 Tensil p. s. i 3, 270 3, 720 3, 660 Elongation, percent 565 595 595 Hysteresis, AT, F 83.9 71. 9 73. 6 Resilience, percent. 61. 5 64. 63. 6 Flex life at 210 F., M 20. 2 34. 3 25.0 Shore hardness. 57 58 59. Compression set, percent 11. 5 11. 0 12.0 Oven Aged 24 Hours at 212 F.:

Stgess-strain properties at 80 1- 300% modulus, p. s. i. 2,130 2,350 2,220 Tensile, p. s. i 3, 760 3, 670 630 Elongation, percent 465 430 Hysteresis, AT, F 68.3 63. 5 64. 9 Resilience, percent. 66. 9 69. 2 68. 3 Flex life 210 F., M... 14. 5 12.0 8. 9 61 63 64 1 30 minutes cure time.

The above data show that liquid polybutadiene is a more effective plasticizer than the commercial products employed and the aged sample is superior in flex life.

The liquid polybutadiene and polyisoprene used in the examples was prepared by mass polymerization methods as set forth hereinbefore.

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit of the disclosure or from the scope of the claims.

Iclaim:

1. The vulcanizable composition of claim 8 wherein said liquid polymer is a polymer of 1,3- butadiene.

2. The vulcanizable composition of claim 8 wherein said liquid polymer is a polymer of 2- methyl-1,3-butadiene.

3. The composition of claim 8 wherein said vulcanizable elastomer is a copolymer prepared by copolymerization of butadiene and styrene monomers in an emulsion system at a temperature of from -20 to 15 C., said butadiene bein present in an amount of from 50 to 85 weight per cent of th total weight of said monomers, and said liquid polymer has a Saybolt Furol viscosity of 100 to 5000 seconds at 100 F. and is present in an amount of from 3 to 25 parts by 14 weight per parts by weight of said vulcanizable elastomer.

4. The composition of claim 3 wherein said liquid polymer is a polymer of 1,3-butadiene.

5. The composition of claim 8 wherein said vulcanizable elastomer is natural rubber, and said liquid polymer is present in an amount of from 3 to 25 parts by weight per 100 parts by weight of said natural rubber.

6. The process of claim 9 wherein said liquid polymer is a polymer of 1,3-butadiene having a Saybolt Furol viscosity of 100 to 5000 seconds at 100 F. and is added in an amount of from 3 to 25 parts by weight per 100 parts by weight of said vulcanizable elastomer.

7. The process of claim 9 wherein said liquid polymer is a polymer of 2-methyl1,3-butadiene having a Saybolt Furol viscosity of 100 to 5000 seconds at 100 F. and is added in an amount of from 3 to 25 parts by weight per 100 parts by weight of said vulcanizable elastomer.

8. A rubber-like, sulfur vulcanizable composition comprising a rubber-like vulcanizable organic elastomer selected from the group consisting of natural rubber and synthetic polymers of conjugated cliolefins; and a liquid polymer prepared from monomers consisting of a 1,3- butadiene selected from the group consisting of 1,3-butadiene and 2-methyl-1,3-butadiene, said. liquid polymer being prepared by mass polymerization in the presence of a catalyst selected from the group consisting of alkali metals and alkali metal hydrides in an amount not exceeding two parts by weight of the total monomers charged and having a particle size less than 200 microns at a temperature in the range from 60 to C.

9. In the process of processing a rubber-like, sulfur vulcanizab-le organic elastomer selected from the group consisting of natural rubber and synthetic polymers of conjugated diolefins to produce elastomer products; that improvement which comprises, adding to said rubber-like vulcanizable organic elastomer as a plasticizer a liquid polymer prepared from monomers consisting of 1,3-butadiene selected from the group consisting of 1,3-butadiene and 2-methyl-1,3- butadiene, said liquid polymer being prepared by mass polymerization in the presence of a catalyst selected from the group consisting of alkali metals and alkali metal hydrides in an amount not exceeding two parts by weight of the total monomers charged and having a particle size less than 200 microns at a temperature in the range from 60 to 110 C.

10. The composition of claim 8 in which the molecular weight of said liquid polymer is between the limits of 800 and 3000 as determined in a solvent.

11. The process of claim 91 in which said liquid polymer has a molecular weight between the limits of 800 and 3000 as determined in a solvent.

WILLIE W. CROUCH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,521,361 Gessler Sept. 5, 1950 FOREIGN PATENTS Number Country Date 492,998 Great Britain Sept. 30, 1938 

8. A RUBBER-LIKE, SULFUR VULCANIZABLE COMPOSITION COMPRISING A RUBBER-LIKE VULCANIZABLE ORGANIC ELASTOMER SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC POLYMERS OF CONJUGATED DIOLEFINS; AND A LIQUID POLYMER PREPARED FROM MONOMERS CONSISTING OF A 1,3BUTADIENE SELECTED FROM THE GROUP CONSISTING OF 1,3-BUTADIENE AND 2-METHYL-1,3-BUTADIENE, SAID LIQUID POLYMER BEING PREPARED BY MASS POLYMERIZATION IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALI METAL HYDRIDES IN AN AMOUNT NOT EXCEEDING TWO PARTS BY WEIGHT OF THE TOTAL MONOMERS CHARGED AND HAVING A PARTICLE SIZE LESS THAN 200 MICRONS AT A TEMPERATURE IN THE RANGE FROM 60 TO 110* C. 